High voltage regulation circuit

ABSTRACT

A high voltage power supply for a cathode-ray tube includes an oscillator intercoupled with a transformer having a high voltage output winding. An additional low voltage winding on the transformer provides a signal substantially proportional to the high voltage output, and such signal is coupled by way of a peak detector to a control amplifier adapted to vary the d.c. bias value in the oscillator circuit. If the high voltage output tends to drop, the peak detector registers the lower voltage, causing the control amplifier to increase the amplitude of oscillations produced by the oscillator to thereby return the high voltage output toward a predetermined value. Since the low voltage winding does not provide a voltage value which is exactly proportional to the high voltage output, additional circuit means is included in series with the high voltage winding for coupling a current feedback to the control amplifier such that an increase in current drawn from the high voltage winding will also cause an increase in the amplitude of oscillations. By this means the actual high voltage output is closely regulated even though the regulation voltage is acquired at a low voltage level in the circuit.

[ 1 June 6, 1972 [54] HIGH VOLTAGE REGULATION CIRCUIT [72] Inventors:Oliver Dalton, Portland; Vaughn Weidel,

Aloha, both of Oreg.

[73] Assignee: Tektronix, Inc., Beaverton, Oreg.

[22] Filed: July 20, 1970 [21] Appl. No.: 64,014

Related 1.1.8. Application Data [63] Continuation-in-part of Ser. No.670,691, Sept. '26,

1967, abandoned.

[52] U.S. Cl. ..321/2, 315/27, 321/19, 331/112 [51 1 Int. Cl. ..I-I02m3/32, H0 1 j 29/70, H03k 3/30 [58] Field ofSearch ..321/22, l8, 19;331/109, 183,

331/112; 315/1, 3, 27; l74/DIG. 11

[56] References Cited OTHER PUBLICATIONS Wireless World, TransistorPower Supplies," L. H. Light, pp. 582- 586, Dec. 1955.

Primary ExaminerWilliam H. Beha, Jr. I Attorney-Buckhorn, Blore,Klarquist and Sparkman [5 7] ABSTRACT A high voltage power supply for acathode-ray tube includes an oscillator intercoupled with a transformerhaving a high voltage output winding. An additional low voltage windingon the transformer provides a signal substantiallyproportional to thehigh voltage output, and such signal is coupled by way of a peakdetector to a control amplifier adapted to vary the dc. bias value inthe oscillator circuit. If the high voltage output tends to drop, thepeak detector registers the lower voltage, causing the control amplifierto increase the amplitude of oscillations produced by the oscillator tothereby return the high voltage output toward a predetermined value.Since the low voltage winding does not provide a voltage value which isexactly proportional to the high voltage output, additional circuitmeans is included in series with the high voltage winding for coupling acurrent feedback to the control amplifier such that an increase incurrent drawn from the high voltage winding will also cause an increasein the amplitude of oscillations. By this means the actualhigh voltageoutput is closely regulated even though the regulation voltage isacquired at a low voltage level in the circuit.

14 Claims, 2 Drawing Figures PATENTEDJUH 6 I972 3,668,505

F IG. 1 [0 CONTROL 28 AMPLIFIER OSCILLATOR 3 /2O 34J I6 22 PEAK DETECTOR3o 32 Ma INVENTORS,

OLIVER DALTON VAUGHN WEIDEL BUG/(HORN, BLORE, KLAROU/ST 8 SPAR/(MANATTORNEYS HIGH VOLTAGE REGULATION CIRCUIT This is a continuation ofapplication, Ser. No. 670,691, filed Sept. 26, 1967, now abandoned.

BACKGROUND OF THE INVENTION A high voltage power supply for acathode-ray tube is an oscilloscope must have good regulation since thecalibration of the instrument is, significantly affected by variation insupply voltage. The calibration of the instrument changes byapproximately the same percentage as a change in the cathode supplyvoltage, thereby tending to cause erroneous readings. Therefore,regulation circuits are employed for holding the cathode voltage asclosely as possible to a predetermined value. The usual circuit includesa voltage divider, one end being connected to the high voltage cathode,and the other end providing a proportional control voltage coupled to aregulation circuit near ground level. The regulation circuit thencontrols the oscillator or means generating the high voltage applied tothe CRT cathode. Such voltage divider must ordinarily be employedbecause of the wide disparity in voltage level usually present betweenthe output and the regulation circuits. Unfortunately, it is difficultto obtain resistors for such a voltage divider which are reliable in thesense of being relatively non-subject to failure, and which at the sametime are capable of providing an accurate control voltage which will notdrift. Resistors which are relatively drift-free are relatively moreprone to failure, and vice versa.

SUMMARY OF THE INVENTION In accordance with an embodiment of the presentinvention, the control voltage for a regulated high voltage powersupply, such as hereinbefore described, is acquired at a low voltagelevel via a low voltage winding means coupled to the power supplytransformer. Therefore, no voltage divider need be employed between highand low voltage points. An ac. voltage is induced in such low voltagewinding means as a result of oscillation current in the transformer, anda peak value of such ac. voltage is produced in a peak detector. Theoutput of the peak detector is in turn applied to a control amplifieremployed for varying the d.c. bias applied to the power supplyoscillator. The amplitude of the oscillations produced is caused toincrease as the power supply high voltage output decreases, and viceversa.

Since the aforementioned control voltage is not acquired at exactly thesame point at which the high voltage output is secured, additionalcircuitry is included to compensate for the efiects of voltage drop andthe like, for example, due to trans former. winding resistance, leakageinductance, power supply rectifier discharge between oscillation cycles,etc. Such addi tional circuitry includes means in series with thetransformer high voltage output winding for supplying an additionalcontrol signal proportional to current drawn from the high voltageoutput winding. Such control signal is applied to the control amplifierin a manner such that the amplitude of oscillations increases as currentdrawn increases, and vice versa.

It is therefore an object of the present invention to provide animproved high voltage regulation circuit wherein the control inputtherefor is derived at a low voltage level.

It is another object of the present invention to provide an improvedhigh voltage regulation circuit which does not employ a conventionald.c. voltage divider between a high voltage level in the circuit and alow voltage control level in the circuit.

It is another object of the present invention to provide an improvedhigh voltage regulation circuit for a cathode-ray tube power supplyemploying an oscillation transformer, wherein the control voltage isderived from a low voltage winding on such transformer.

The subject matter which we regard as our invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. The invention, however, both as to organization andmethod and operation, together with further advantages and objectsthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings whereinlike reference characters refer to like elements.

DRAWINGS FIG. 1 is a block diagram of a high voltage regulation circuitaccording to the present invention; and

FIG. 2 is a schematic diagram of such a high regulation circuit.

DETAILED DESCRIPTION Referring to the drawings, and particularly to FIG.I, a power supply for a cathode-ray tube 10 includes an oscillator 12having an oscillator output winding 14 and a feedback winding 16inter-coupled by means of high voltage transformer 18. High voltagetransformer 18 also has wound thereupon a high voltage secondary winding20, one terminal of which is coupled to cathode 22 of cathode-ray tube10, through negatively poled diode 24. The opposite end of high voltagesecondary 20 is connected to ground through an impedance taking the formof a resistor 26. A filter capacitor 28 is connected between suchopposite end of the high voltage secondary and the anode of diode 24.The turns ratio of transformer 18 is such that during operation ofoscillator 12 a high pulsating voltage tends to be induced in winding20. Because of the rectifying action of diode 24, a high negativevoltage appears at cathode 22 relative to ground.

According to the present invention, regulation circuitry which suitablyincludes a peak detector 30 receives an input from a control winding 32,the latter also being coupled to transformer 18, and the aforementionedpeak detector is constructed to measure the peak value of the controlvoltage induced in winding 32. Winding 32 is a low voltage winding, andis suitably grounded at one end as indicated, but the voltage inducedtherein is approximately proportional to the output of the oscillator 12and also approximately proportional to the high voltage induced inwinding 20. Control amplifier 34, receiving the output of peak detector30, operates to decrease the bias of oscillator 12, allowing theamplitude of the oscillations produced to increase, as the voltage atpeak detector 30 decreases. Similarly, if the high voltage output tendsto rise, the voltage at peak detector 30 causes control amplifier 34 toincrease the bias of oscillator 12 in order to reduce the amplitude ofthe oscillations produced. Since the voltage provided at peak detector30 is substantially proportional to the high voltage output of thesupply, the operation of the circuit tends to compensate for such highvoltage output changes as may tend to occur.

As indicated above, the control voltage is acquired atwinding 32, whichis at a low voltage level in the circuit, and therefore a voltagedivider between high voltage cathode 22 and control amplifier 34 is notrequired. However, since winding 32 is not at exactly the same circuitlocation as cathode 22, additional means are employed to compensate forsuch intermediate voltage drops as may occur. Such circuit meanscomprises an impedance, here taking the form of resistor 26, in serieswith high voltage winding 20. A connection 36 couples the juncturebetween resistor 26 and winding 20 to control amplifier 34. As increasedcurrent is drawn by cathode 22 through winding 20 and resistor 26, achange in voltage will take place across resistor 26 and this change iscoupled to the control amplifier for in turn causing the controlamplifier to increase the amplitude of oscillations produced byoscillator 12. Similarly, if the current drawn decreases, the amplitudeof oscillation is caused to decrease. This circuit therefore tends tocompensate for differences in proportionality between the voltage acrosswinding 32 and at cathode 22, for example due to transformer windingresistance, transformer leakage inductance, discharging of diode 24 andcapacitor 28 between oscillation cycles, and intermediate resistance inthe circuit.

A more detailed circuit diagram of a high voltage regulation circuit inaccordance with the present invention is illustrated in FIG. 2, whereinsimilar elements are referred to by like reference numerals. Hereoscillator 12 comprises an NPN transistor 38 having its collectorconnected to a positive source through transformer oscillator outputwinding 14 in series with choke 40. The juncture between choke 40 andwinding 14 is bypassed to ground employing capacitor 39. A firstterminal of feedback winding 16, also wound on the same transformer, isconnected to the base of transistor 38 while the remaining terminal ofthe winding is coupled to the transistor emitter through capacitor 42.The emitter of transistor 38 is suitably grounded. I

High voltage winding 20 is connected at a first end thereof to a sourceof predetermined positive voltage at terminal 43 through an impedancecomprising resistor 26 and capacitor 44 in parallel. The opposite end ofwinding 20 is coupled through negatively poled diode 24 and filterresistor 46 to cathode 22 of cathode-ray tube 10. A filter capacitor 28is interposed between the anode of diode 24 and the juncture betweenresistor 26 and winding 20. A similar filter capacitor 48 is connectedbetween cathode 22 and ground, and capacitor 48 is shunted by a voltagedivider 50 including focus control 52 in series therewith.

A second high voltage winding 54 is also inductively related totransformer 18 and preferably has a similar number of turns, e.g. aslightly greater number than winding 20. Winding 54 is also preferablywound in a bifilar manner with winding 20. One end of winding 54 isconnected through negatively poled diode 56 and resistor 58 in series togrid 60 of the cathode-ray tube. The remaining end of winding 54 isconnected through resistor 62 to input terminal 64, and a voltagedivider 66 is disposed between terminal 64 and grid 60. Filtercapacitors 61 and 63 join similarly oriented ends of resistors 58 and62. Both windings 20 and 54 are high voltage windings and have arelatively large number of turns as compared with the other windingsdescribed.

Winding 54, together with diode 56, capacitors 61 and 63, as well asresistances 58, 62, and 66 form a floating power supply between terminal64 and grid 60. The purpose of this power supply is to elevate a Z-axissignal applied to terminal 64 to the voltage level desired for grid 60.This voltage level is desirably slightly negative with respect tocathode 22. An additional low voltage winding 68 is suitably provided ontransformer 18 for supplying filament power to the cathode-ray tube.

' In the circuit of FIG. 2, as thus far described, oscillator 12produces oscillations in the form of a series of pulses or surgesresulting from the feedback coupling provided by the transformer fromoscillator output winding 14 to feedback winding 16. During operation ofthe oscillator, the juncture between This negative voltage isattributable to rectification at the I base-emitter junction oftransistor 38, and storage of such voltage upon capacitor 42. Thisnegative dc. bias potential determines the amplitude of oscillationsproduced by oscillator 12 since the bias is added to the feedback fromwinding 16, it being understood that transistor 38 is not allowed to gointo collector saturation.

As a result of oscillator operation, a high voltage is induced inwinding 20, and, of course, also in winding 54. Diode 24 is poled suchthat a negative high voltage, for example a negative 3 kilovolts, isapplied to cathode 22, while a negative 3.05 kilovolt bias is similarlyapplied to grid 60 by virtue of rectification in diode 56. The end ofwinding 20 opposite diode 24 is connected through the parallelcombination of resistor 26 and capacitor 44 to a predetermined smallpositive voltage applied at terminal 43, which voltage is relativelyclose to ground level. For example, this voltage is suitably maintainedat a value equaling a positive 15 volts with respect to ground. Thediode 24, together with capacitors 28 and 48 as well as resistor 46 anddivider 50, produce a rectifying and filtering action for the voltageapplied to cathode 22, such that this voltage is substantially do.

As hereinbefore described, during operation of high voltage cathode-raytube power supply the voltage on the cathode is apt to vary, as, forexample, when a variable amount of current is drawn from cathode 22.However, in a high quality oscilloscope it is desired that the cathodevoltage be constant within 0.5 percent so that the instrument'scalibration will be accurate. Therefore, regulation circuitry is alsoutilized herein, but this regulation circuitry does not employ a voltagedivider between the high voltage and lower voltage level components.Rather, the control voltage is acquired at a low level, here at controlwinding 32. One end of this low voltage winding is grounded and agrounded electrostaticshield 69 is also suitably located between winding32 and the transformer. The control voltage, acquired across winding 32,is applied to a peak detector 30 including a positively poled diode 70connecting the ungrounded terminal on winding 32 to a storage capacitor72, the opposite end of capacitor 72 being grounded. As the oscillator12 produces oscillations, voltage is induced in winding 32 and diode 70rectifies the resulting current so that the ungrounded end of capacitor72 charges to a positive value. Very little current is drawn from thiscapacitor, and, hence, capacitor 72 charges to substantially the peakvalue of voltage induced in winding 32. The peak value of the voltageinduced in winding 32 is substantially applied to the base of PNPtransistor 74, the latter comprising the principal element of controlamplifier 34. The voltage drops across diode 70 and the base-emitterjunction of transistor 74 cancel, and also the effects of temperaturechanges upon these junctions tend to cancel.

Transistor 74 of control amplifier 34 has its emitter connected to thejuncture between resistor 26 and high voltage winding 20, while the baseof transistor 74 is returned to ground through resistor 76. Thecollector of transistor 74 is coupled to the junction of capacitor 42and feedback winding 16 of the oscillator by means of resistors 78 and80 disposed serially therebetween in that order. A shunting circuit isprovided for capacitor 42 of oscillator 12 and comprises a controldevice in the form of an NPN transistor 82 having its emitter connectedto the junction between capacitor 42 and winding 16, and having its baseconnected to the junction between resistors 78 and 80. The collector oftransistor 82 is connected to the cathode of diode 84, the anode ofwhich is connected to ground.

During operation ofthe regulation circuitry, the low level controlvoltage induced in winding 32 is applied to peak detector 30 whichprovides the input for control amplifier 34. Control amplifier 34, inturn, provides a control signal at the collector of transistor 74 forvarying the current in resistors 78 and 80 in correspondence with thepeak value of the control voltage so that the voltage at the base oftransistor 82 is similarly varied. Transistor 82 shunts capacitor 42 toa greater or lesser degree as determined by its base voltage so as toproportionately determine the bias voltage for the oscillator 12provided across capacitor 42.

Assume, for example, that the high voltage induced in winding 20decreases. Therefore the lower voltage value across winding 32 willsubstantially proportionately decrease whereby a lower peak voltage ispresent across capacitor 72 and likewise upon the base electrode oftransistor 74. Since the base of transistor74 is negative-going relativeto the transistors positive emitter, a greater current will flow throughthe transistor and in resistors 78 and 80, raising the level of the baseof transistor 82 with respect to its emitter. As a result, transistor 82becomes more conductive, shunting capacitor 42 to a greater degree, andreducing the negative bias voltage thereacross. Therefore, the amplitudeof oscillations delivered to oscillator output winding 14 will increase.Accordingly, the high voltage output will return toward its desiredvalue. Of course, the reverse voltage changes take place should the highvoltage output undesirably rise.

In this regulation circuit, amplifier 34 is provided with a comparisonvoltage through the parallel combination of resistor 26 and capacitor44. Here, this comparison voltage is a positive volts, but, of course,some other suitable value may be selected. The selected value shouldnaturally be quite stable. The impedance of resistor 26 is quite small,so that substantially the same value applied at terminal 43 is alsoapplied to the emitter of transistor 74. As a result of comparisonbetween the voltage at terminal 43 and the peak voltage across capacitor72 by transistor 74, a control signal is provided at the collector oftransistor 74 for application to the oscillator circuit via transistor82. The overall circuit will operate in the manner so as to maintainsubstantially the voltage value applied at terminal 43, e.g. 15 volts,as the voltage across winding 32, and this voltage determines, throughthe turns ratio of the transformer, the voltage appearing at the otherwindings.

Since the voltage across winding 32 is not precisely the output voltageapplied to cathode 22 as multiplied by the turns ratio between windingand winding 32, additional circuitry is utilized to compensate for thisdifference. The voltage at cathode 22 can have become reduced by theresistance of winding 20, leakage inductance of the transformer, voltagedrop in diode 24 and resistor 26 as well as associated conductors, andalso due to the discharge of the circuit comprising diode 24 andcapacitor 28 between cycles. Accordingly, a current feedback circuit isprovided which includes an impedance comprising the parallel combinationof resistor 26 and capacitor 44 between the positive or upper end ofwinding 20 and terminal 43. As current drawn at cathode 22 ofcathode-ray tube 10 increases, the voltage across resistor 26 changes bya proportional amount, thereby altering the comparison voltage appliedat the emitter of transistor 74 of the control amplifier. The polarityof the connection is such that an increase in current to cathode 22raises the voltage at the emitter of transistor 74, since the voltagedrop across resistor 26 due to current in winding 20 is the reverse ofthe voltage drop due to current flowing toward the emitter of transistor74 from terminal 43. As a result of this increase in voltage at theemitter of transistor 74, the current increases in the transistorscollector circuit, that is, the current increases through resistors 78and 80. The voltage at the base of transistor 82 will rise, diminishingthe negative oscillator bias developed across capacitor 42. Therefore,the oscillator feedback reaching the emitter of transistor 38 willincrease and the amplitude of oscillations will increase. As a resultthe voltage provided at high voltage winding 20 will increase-as thecurrent drawn by cathode 22 increases, whereby to compensate for voltagedrops, for example, between the transformer and the cathode 22. Resistor26 in the current feedback circuit is paralleled by capacitor 44 tosmooth out ripple otherwise likely to occur thereacross because of theoscillating nature of the voltage which is induced in high voltagewinding 20.

As initially connected for operation, no ac. voltage is developed acrossthe windings of transformer 18, since no oscillation has been takingplace in oscillator 12. Therefore, the ungrounded end of winding 32 isat ground potential, and the base of transistor 74 is similarlynearground. Resistor 76 provides sufficient base current for transistor 74such that this transistor saturates. Also, the value of resistor 78 ischosen to provide sufficient current to start the oscillator. Thejunction between resistors 78 and 80 rises to a voltage which is the sumof the biased base-emitter drops of transistors 82 and 38. The

emitter of transistor 82 will be slightly above ground or positive.Diode 84 is non-conducting at this time, permitting transistor 82 to beelevated above ground potential. The base of transistor 38 is alsoraised to a positive voltage, causing the initiation of oscillation. Theroute for the oscillator starting current through resistor 78 is thenthrough the base-emitter junction of transistor 82, paralleled byresistor 80, and through feedback winding 16 to the base of transistor38. After oscillations start, the hereinbefore described bias isdeveloped across capacitor 42, and the emitter of transistor 82 dropsbelow ground level. Therefore, diode 84 resumes its normally conductivestate, and transistor 82 operates as a control device for shuntingcapacitor 42.

Various changes can be made in the circuit according to the presentinvention. For example, peak detector 30 could be replaced with apeak-to-peak-detector if so desired. Moreover, although winding 32 isshown as a separate and distinct low voltage winding on transformer 18,it is appreciated that this winding could form a low voltage portion ofsome other winding near ground level, with the circuit being alteredaccordingly.

While we have shown and described preferred embodiments of my invention,it will. be apparent to those skilled in the art that many other changesand modifications may be made without departing from our invention inits broader aspects. We therefore intendthe appended claims to cover allsuch changes and modifications as fall within the true spirit and scopeof our invention.

We claim:

1. In a high voltage power supply including an oscillator circuitemploying a step-up transformer with a high voltage winding from which ahigh voltage output is derived, the improvement comprising a regulationcircuit for said power supply including:

first low voltage winding means on said transformer for deriving a firstvoltage from said transformer substantially proportional to said highvoltage output,

second control circuit means for comparing said first voltage with apredetermined voltage to obtain a control signal,

third control circuit means for applying said control signal to saidoscillator circuit for continuously controlling the amplitude ofoscillations produced thereby in a sense for compensating for voltagechanges in said high voltage output,

and fourth means comprising an impedance connected in series with saidhigh voltage winding which is responsive to current drawn from said highvoltage winding for also varying the amplitude of said oscillations suchthat said amplitude increases as said current increases, and decreasesas said current decreases.

2. The circuit according to claim 1 including a peak detector employinga rectifier for receiving the output of said low voltage winding andapplying the same as an input to said second control circuit means.

3. The circuit according to claim 1 wherein said oscillator includesoutput and feedback windings on said transformer and wherein saidoscillator receives a dc. voltage bias in series with said feedbackwinding.

- 4. The circuit according to claim 1 wherein said low voltage windingmeans comprises a winding distinct from othe windings on saidtransformer.

5. The circuit according to claim 2 wherein said oscillator includes afeedback winding and a coupling capacitor therefor, said circuit furtherincluding a control device shunting said coupling capacitor andreceiving the output of said amplifier to vary the degree of shunting ofsaid coupling capacitor under the control of said second control circuitmeans.

6. A high voltage power supply comprising:

a transformer having a high voltage output winding, an

oscillator output winding, a feedback winding, and a control winding,

oscillator means comprising an amplifying device having an outputterminal coupled to said oscillator output winding and an input terminalcoupled to said feedback winding,

an amplifier having its input coupled to said control winding forreceiving an input voltage therefrom and comparing the same with acomparison voltage to produce an output representative of thecomparison, such output being coupled to control a bias voltage appliedto the amplifying device of said oscillator means,

and an impedance connected in series with said high voltage winding forproviding thereacross at least a portion of the comparison voltagecoupled to said amplifier.

men 01 An 7. The circuit according to claim 6 including a capacitor inseries with said feedback winding for developing a bias voltage, and ashunting device coupled across said capacitor and controlled by theoutput of said amplifier to vary said bias voltage.

8. A high voltage power supply comprising: 7

a transformer having a high voltage output winding, an

oscillator output winding, a feedback winding, and a control winding,

oscillator means comprising a transistor having its base coupled to saidfeedback winding and having its collector coupled to said oscillatoroutput winding,

a capacitor disposed in series with said feedback winding and theemitter of said transistor, for developing a bias voltage,

an amplifier having an input coupled to said control winding forreceiving an input voltage therefrom and comparing the same with acomparison voltage to produce an output representative of thecomparison,

an impedance connected in series with said high voltage winding forproviding thereacross at least a portion of the comparison voltagecoupled to said amplifier,

and a shunting device coupled across said capacitor, said shuntingdevice comprising a shunting transistor having its collector-emitterpath and a diode in series therewith shunted across said capacitor, withsaid diode being located between said collector-emitter path and theemitter of the first mentioned transistor, said diode being polednormally to pass current to said shunting transistor, the base of saidshunting transistor receiving the output of said amplifier forcontrolling the bias voltage of the first mentioned transistor.

9. A high voltage power supply comprising:

a transformer having a high voltage output winding, an

oscillatoroutput winding, a feedback winding, and a control winding,

oscillator means comprising an amplifying device having an outputterminal coupled to said oscillatoroutput winding and an input terminalcoupled to said feedback winding,

an amplifier having its input coupled to said control winding forreceiving an input voltage therefrom and comparing the same with acomparison voltage to produce an output representative of thecomparison, such output being coupled to control a bias voltage appliedto the amplifying device of said oscillator means,

a series diode interposed between said control winding and the input tosaid amplifier, and a capacitor coupled across the input of saidamplifier, to develop at the input of said amplifier a peak value ofvoltage induced across said control winding,

and an impedance coupled in series with said high voltage winding forproviding thereacross at least a portion of the comparison voltagecoupled to said amplifier.

10. The circuit according to claim 9 wherein said amplifier comprises atransistor having its base connected to said diode, its collectorcoupled to control the bias voltage of said oscillator, and including aresistor and capacitor in parallel between the emitter of saidtransistor and a source of comparison voltage to form said impedance,

and including means coupling said high voltage winding to said emitterof said transistor.

11. A high voltage power supply for a cathode-ray tube comprising:

a transformer having a high voltage output winding, an

oscillator output winding, a feedback winding, and a control winding,

a rectifying diode for coupling a first end of said high volt agewinding to the cathode of said cathode-ray tube to provide a high dc.voltage at said cathode,

oscillator means having an output terminal coupled to said oscillatoroutput winding, and an input terminal coupled to said feedback winding,

an amplifier having its output coupled to control a bias voltage appliedto said oscillator means, said amplifier acting to compare its inputwith a comparison voltage to produce an output representative of thecomparison,

a second diode coupling said control winding to an input of saidamplifier, and a capacitor coupled across the input of said amplifier,to develop, as the input of said amplifier, a peak value of voltageinduced across said control windmg,

and an impedance connected in series with the second end of said highvoltage winding for providing thereacross at least a portion of acomparison voltage for said amplifier,

said amplifier comprising a transistor having its base connected to saidsecond diode, its collector coupled to control the bias voltage of saidoscillator, and its emitter coupled to the second end of said highvoltage winding.

12. The circuit according to claim 11 including a second capacitor inseries with said feedback winding for developing the bias voltage forsaid oscillator means, and a shunting device coupled across said secondcapacitor and controlled by the output of said amplifier to vary saidbias voltage,

said oscillator means comprising a transistor having its base coupled tosaid feedback winding, its emitter coupled to said feedback windingthrough said second capacitor, and having its collector coupled to saidoscillator output winding,

said shunting device comprising a shunting transistor having itscollector-emitter path, and a third diode in series therewith, shuntedacross said second capacitor, with said third diode being locatedbetween said collector-emitter path and the emitter of the oscillatormeans transistor, wherein said third diode is poled normally to passcurrent to said shunting transistor, the base of said shuntingtransistor receiving the output of said amplifier,

13. A high voltage power supply for a cathode-ray tube comprising:

' a transformer having a high voltage output winding, an

oscillator output winding, a feedback winding, and a control winding,

a rectifying diode for coupling a first end of said high voltage windingto the cathode of said cathode-ray tube to provide a high dc. voltage atsaid cathode,

oscillator means having an output terminal coupled to said oscillatoroutput winding, and an input terminal coupled to said feedback winding,

an amplifier having its output coupled to control a bias voltage appliedto said oscillator means, said amplifier acting to compare its inputwith a comparison voltage to produce an output representative of thecomparison,

means coupling an integrated value of the voltage induced across saidcontrol winding as the input to said amplifier,

and an impedance connected in series with the second end of said highvoltage winding for providing thereacross at least a portion of thecomparison voltage for said amplifier, the remaining end of saidimpedance being connected to a reference potential.

14. A high voltage power supply for deriving a constant high dc. voltagefor a cathode-ray tube, said power supply including an oscillator, astep-up transformer having a low voltage primary winding and a highvoltage secondary winding for stepping up the output of the oscillator,and means for rectifying and smoothing the output voltage at thesecondary winding for application to said cathode-ray tube, theimprovement comprising:

control means for controlling the output amplitude of said oscillator bycontrolling the bias circuit of the oscillator,

a low voltage winding coupled to the step-up transformer for drivingsaid control means, said low voltage winding deriving thereacross avoltage substantially proportional to the high voltage output of thepower supply,

a parallel combination of a resistor and capacitor connected in serieswith the high voltage secondary winding of the step-up transformer fordetecting the quiescent load cur- 3 ,668,505 9 l rent, said controlmeans also being driven by the voltage developed across said parallelcombination.

l l U! I0!

1. In a high voltage power supply including an oscillator circuitemploying a step-up transformer with a high voltage winding from which ahigh voltage output is derived, the improvement comprising a regulationcircuit for said power supply including: first low voltage winding meanson said transformer for deriving a first voltage from said transformersubstantially proportional to said high voltage output, second controlcircuit means for comparing said first voltage with a predeterminedvoltage to obtain a control signal, third control circuit means forapplying said control signal to said oscillator circuit for continuouslycontrolling the amplitude of oscillations produced thereby in a sensefor compensating for voltage changes in said high voltage output, andfourth means comprising an impedance connected in series with said highvoltage winding which is responsive to current drawn from said highvoltage winding for also varying the amplitude of said oscillations suchthat said amplitude increases as said current increases, and decreasesas said current decreases.
 2. The circuit according to claim 1 includinga peak detector employing a rectifier for receiving the output of saidlow voltage winding and applying the same as an input to said secondcontrol circuit means.
 3. The circuit according to claim 1 wherein saidoscillator includes output and feedback windings on said transformer andwherein said oscillator receives a d.c. voltage bias in series with saidfeedback winding.
 4. The circuit according to claim 1 wherein said lowvoltage winding means comprises a winding distinct from other windingson said transformer.
 5. The circuit according to claim 2 wherein saidoscillator includes a feedback winding and a coupling capacitortherefor, said circuit further including a control device shunting saidcoupling capacitor and receiving the output of said amplifier to varythe degree of shunting of said coupling capacitor under the control ofsaid second control circuit means.
 6. A high voltage power supplycomprising: a transformer having a high voltage output winding, anoscillator output winding, a feedback winding, and a control winding,oscillator means comprising an amplifying device having an outputterminal coupled to said oscillator output winding and an input terminalcoupled to said feedback winding, an amplifier having its input coupledto said control winding for receiving an input voltage therefrom andcomparing the same with a comparison voltage to produce an outputrepresentative of the comparison, such output being coupled to control abias voltage applied to the amplifying device of said oscillator means,and an impedance connected in series with said high voltage winding forproviding thereacross at least a portion of the comparison voltagecoupled to said amplifier.
 7. The circuit according to claim 6 includinga capacitor in series with said feedback winding for developing a biasvoltage, and a shunting device coupled across said capacitor andcontrolled by the output of said amplifier to vary said bias voltage. 8.A high voltage power supply comprising: a transformer having a highvoltage output winding, an oscillator output winding, a feedbackwinding, and a control winding, oscillator means comprising a transistorhaving its base coupled to said feedback winding and having itscollector coupled to said oscillator output winding, a capacitordisposed in series with said feedback winding and the emitter of saidtransistor, for developing a bias voltage, an amplifier having an inputcoupled to said control winding for receiving an input voltage therefromand comparing the same with a comparison voltage to produce an outputrepresentative of the comparison, an impedance connected in series withsaid high voltage winding for providing thereacross at least a portionof the comparison voltage coupled to said amplifier, and a shuntingdevice coupled across said capacitor, said shunting device comprising ashunting transistor having its collector-emitter path and a diode inseries therewith shunted across said capacitor, with said diode beinglocated between said collector-emitter path and the emitter of the firstmentioned transistor, said diode being poled normally to pass current tosaid shunting transistor, the base of said shunting transistor receivingthe output of said amplifier for controlling the bias voltage of thefirst mentioned transistor.
 9. A high voltage power supply comprising: atransformer having a high voltage output winding, an oscillator outputwinding, a feedback winding, and a control winding, oscillator meanscomprising an amplifying device having an output terminal coupled tosaid oscillator output winding and an input terminal coupled to saidfeedback winding, an amplifier having its input coupled to said controlwinding for receiving an input voltage therefrom and comparing the samewith a comparison voltage to produce an output representative of thecomparison, such output being coupled to control a bias voltage appliedto the amplifying device of said oscillator means, a series diodeinterposed between said control winding and the input to said amplifier,and a capacitor coupled across the input of said amplifier, to developat the input of said amplifier a peak value of voltage induced acrosssaid control winding, and an impedance coupled in series with said highvoltage winding for providing thereacross at least a portion of thecomparison voltage coupled to said amplifier.
 10. The circuit accordingto claim 9 wherein said amplifier comprises a transistor having its baseconnected to said diode, its collector coupled to control the biasvoltage of said oscillator, and including a resistor and capacitor inparallel between the emitter of said transistor and a source ofcomparison voltage to form said impedance, and including means couplingsaid high voltage winding to said emitter of said transistor.
 11. A highvoltage power supply for a cathode-ray tube comprising: a transformerhaving a high voltage output winding, an oscillator output winding, afeedback winding, and a control winding, a rectifying diode for couplinga first end of said high voltage winding to the cathode of saidcathode-ray tube to provide a high d.c. voltage at said cathode,oscillator means having an output terminal coupled to said oscillatoroutput winding, and an input terminal coupled to said feedback winding,an amplifier having its output coupled to control a bias voltage appliedto said oscillator means, said amplifier acting to compare its inputwith a comparison voltage to produce an output representative of thecomparison, a second diode coupling said control winding to an input ofsaid amplifier, and a capacitor coupled across the input of saidamplifier, to develop, as the input of said amplifier, a peak value ofvoltage induced across said control winding, and an impedance connectedin series with the second end of said high voltage winding for providingthereacross at least a portion of a comparison voltage for saidamplifier, said amplifier comprising a transistor having its baseconnected to said second diode, its collector coupled to control thebias voltage of said oscillator, and its emitter coupled to the secondend of said high voltage winding.
 12. The circuit according to claim 11including a second capacitor in series with said feedback winding fordeveloping the bias voltage for said oscillator means, and a shuntingdevice coupled across said second capacitor and controlled by the outputof said amplifier to vary said bias voltage, said oscillator meanscomprising a transistor having its base coupled to said feedbackwinding, its emitter coupled to said feedback winding through saidsecond capacitor, and having its collector coupled to said oscillatoroutput winding, saId shunting device comprising a shunting transistorhaving its collector-emitter path, and a third diode in seriestherewith, shunted across said second capacitor, with said third diodebeing located between said collector-emitter path and the emitter of theoscillator means transistor, wherein said third diode is poled normallyto pass current to said shunting transistor, the base of said shuntingtransistor receiving the output of said amplifier.
 13. A high voltagepower supply for a cathode-ray tube comprising: a transformer having ahigh voltage output winding, an oscillator output winding, a feedbackwinding, and a control winding, a rectifying diode for coupling a firstend of said high voltage winding to the cathode of said cathode-ray tubeto provide a high d.c. voltage at said cathode, oscillator means havingan output terminal coupled to said oscillator output winding, and aninput terminal coupled to said feedback winding, an amplifier having itsoutput coupled to control a bias voltage applied to said oscillatormeans, said amplifier acting to compare its input with a comparisonvoltage to produce an output representative of the comparison, meanscoupling an integrated value of the voltage induced across said controlwinding as the input to said amplifier, and an impedance connected inseries with the second end of said high voltage winding for providingthereacross at least a portion of the comparison voltage for saidamplifier, the remaining end of said impedance being connected to areference potential.
 14. A high voltage power supply for deriving aconstant high d.c. voltage for a cathode-ray tube, said power supplyincluding an oscillator, a step-up transformer having a low voltageprimary winding and a high voltage secondary winding for stepping up theoutput of the oscillator, and means for rectifying and smoothing theoutput voltage at the secondary winding for application to saidcathode-ray tube, the improvement comprising: control means forcontrolling the output amplitude of said oscillator by controlling thebias circuit of the oscillator, a low voltage winding coupled to thestep-up transformer for driving said control means, said low voltagewinding deriving thereacross a voltage substantially proportional to thehigh voltage output of the power supply, a parallel combination of aresistor and capacitor connected in series with the high voltagesecondary winding of the step-up transformer for detecting the quiescentload current, said control means also being driven by the voltagedeveloped across said parallel combination.